The invention concerns an optical Fourier transform (FT) spectrometer with optical means, installed inside the spectrometer housing, for guiding a beam of radiation from an internal radiation source, via a two-beam interferometer and a sample device, to an internal signal receiver with at least one entrance for the optional deflecting-in of a beam of radiation from an external radiation source into the spectrometer housing and internally movable optical means to guide this deflected-in beam of radiation to the interferometer and at least one exit for the optional deflecting of the beam of radiation coming out of the interferometer, via movable internal optical means, out of the spectrometer housing to an external sample device.
Such a Fourier spectrometer is, for example, known from the company publication "IFS 66" (Jan. 1992) of the company Bruker Analytische Mess technik GmbH.
Infrared (IR) spectroscopy fundamentally requires, in order to effect a usable result, the preparation of the measurement sample in a form or its location in a position, where it is accessible to a spectrometer measuring beam. In wide-spread laboratory analysis, the sample is usually embedded in either a solid or fluid matrix. A non-absorbing, pulverized salt is often utilized as a solid matrix with which the pulverized sample is pressed into a tablet, which is then introduced into the sample beam for a transmission measurement.
A suitable solvent is utilized as a fluid matrix which exhibits only a small self-absorption and in which the sample can be completely dissolved. The solution is introduced into an optical cell which is then subjected to the measuring beam for a transmission measurement.
For these types of standard measurements, the space which is available in the sample region of the spectrometer is completely sufficient. Likewise the accessories for somewhat more difficult measurement procedures, such as devices for granulates, fibers, and foils, usually have sufficient space in the sample region.
There are, however, a plurality of substances which cannot be prepared for a measurement with the assistance of these standard sample preparation measures. Included therein are gaseous samples, samples which must be cooled or heated, or samples whose dimensions are too large for the sample region. In order to spectroscopically measure samples of this kind it is necessary to utilize an appropriate accessory in or on which the sample can be arranged, and by means of which the measuring beam can be introduced onto the sample. Since, due to space limitations, such an accessory cannot be accommodated in the sample region of the spectrometer optics, it is necessary to position it outside of the spectrometer housing, whereby the measuring beam is guided out of the spectrometer optics.
Due to the large detection sensitivity offered by the FT-method, special measuring devices are utilized for a plurality of applications, the devices being preferentially arranged outside of the spectrometer optics. Included therewith are, for example, an IR measuring microscope, coupling between the spectrometer and a gas chromatograph (GC), or the connection to a measuring accessory for Raman measurements. Due to the enormous amount of collected information accessed by the FT-method, more and more extensive accessory units are being increasingly utilized which, due to their space requirements, are arranged outside the spectrometer housing.
Increasingly, the possibility of connection to not only a single, but rather to a plurality of external units is being required, among which the measurement beam, via switching mirrors, can be directed. For reasons of operational simplicity the switching is controlled by a computer via servo devices. An example for the connection of a plurality of units is a GC-IR-coupling, an IR-microscope, and a Raman accessory.
There is also an increasing demand for the capability of accepting measurement radiation from an external signal source such as, for example, a discharge lamp, a photoluminescense accessory or a distant radiation source. In these cases, it is necessary that an appropriate radiation entrance be available in the spectrometer optics.
Due to the plurality of needs in current analytic and research laboratories, a plurality of beam exit and entrances are desirable. Since for each such exit or entrance, a separate connection as well as an appropriate computer-controlled beam switching device must be available, an optical system with more than a total of approximately two external connection possibilities each, is very complicated. The current prior art is represented by the above mentioned spectrometer IFS 66.
This known Fourier spectrometer has up to three exits (external sample beams) and two entrances for external radiation sources. These entrances and exits can optionally be accessed through the displacement or tilting of mirrors in the spectrometer. Thereby it is possible to introduce into the spectrometer light from the external radiation sources which are to be examined, whereby in the experimental arrangement up to two radiation sources can be permanently provided for. By means of the up to three exits, it is possible to couple the spectrometer with other analytic methods, for example, GC, TGA (Thermal Gravimetric Analysis), TLC (Thin Layer Chromatography) and the like. However, for reasons of construction the entrances and exits per se are each fixed. This limits the flexibility of the operator. It is, for example, not possible for him to decouple a completed experiment from one exit and then couple-in, at this position, radiation from a newly assembled experiment, or, for example, to construct a configuration with (for example) five external radiation sources among which the spectrometer can be switched.
There is therefore a need for a more flexible Fourier spectrometer with which an increased possibility of combinations of external sources or detection means is given, access to which is facilitated by simple switching in the spectrometer.
It is the purpose of the invention to further improve a spectrometer of the above mentioned kind in such a fashion that the compact shape of the spectrometer is maintained and in that, by means of a simple switching in the spectrometer, at least one, and preferentially all entrances can also be utilized as exits and vice versa.